This invention generally relates to packaging machines, particularly to packaging machines in which a thermoplastic packaging foil is heated to its thermoplastic state by contacting one surface thereof with the surface of a heated plate.
Conventional packaging machines using heated thermoplastic foils have a heating plate for contacting one surface of the packaging foil to heat the same to its thermoplastic state. In order to prevent inclusions of air between the heating plate and the foil, the heated contacting surface of the plate is provided with narrow grooves or channels to vent any residual air. The grooves or channels are connected with venting openings extending through the heating plate. Providing the heating plate with this kind of venting channels substantially increases the manufacturing cost and therefore is undesirable.
Another attempt to prevent the inclusion of residual air between the heating plate and the foil is to provide the contacting surface of the heating plate with a pattern of projecting or raised members. In this case, however, the foil will only contact these raised members so that it cannot be heated in uniform manner and will show a structure corresponding to the pattern of the raised members. This is obviously undesirable for many purposes.